DPPA researchBy Gefei Wang

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Foil cover of waste liquid beaker:One of the major liquid used in lab is ethanol,

which is volatile and inflammable. So it is

important to cover the beaker to prevent ethanol

gas from flowing out. And when you find the foil

has holes or cannot cover the beaker, please

make a new cover, it only takes 1min .

Lab safety

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Aspirator:When aspirator fall on the floor, its tip may

touch the dirt on the floor. And the

contaminated tip will affect the experiment

results.

Once you finish using aspirator, please put it

to clean area, like the top of the black box,

or the board.

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1,Work in the lab under instruction of Ting

2,Learn basic knowledge about surface lipid interaction

3,Practice technique of measuring surface pressure

What I do this semester

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WHAT I’VE LEARNED…

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IntroductionAerosols play an important role in climate change, so it is necessary to understand the its property and behavior. The majority of aerosols come from ocean, and ocean surface is covered by SSML which affect the formation of aerosols and interact with the aerosol surface. To studyaerosol surface, DPPA is selected as model system.

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DPPA (dipalmitoyl-phosphatidic acid):-has two 16 C chains-strong intermolecular force-contains phosphate group

Model system DPPA

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Why DPPA?

First• SSML contain plenty of

fatty acid, and the most abundant is C16 fatty acid, palmitic acid(PA)

• PA is component of DPPA

Second• DPPA itself is

intermediate phospholipid

• Study DPPA held understand more complex lipid molecule

Third• DPPA contains no

moieties on its phosphate

• So it is simple and easy to study

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InstrumentLangmuir trough: used to compress monolayers of molecules on the surface of a given sub phase (usually water),

During compressing, density of the monolayer changes. This results in surface pressure change, which can be sensed by the tensiometer.

Lab technique

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Method: Langmuir-Wilhelmy balance (LWB) -Used to measure the surface tension-the compression of barrier changes the distance between molecule in monolayer-so the surface pressure change, and is detect by Wilhelmy plate.

𝜋=𝛾𝑤−𝛾 𝑠

Surface tension of subphase

Surface tension of subphase with monolayer

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=--net force -F width -W, and thickness-T, the contact angle-θ

Assume plate is thin enough, and is completely wetted to ensure a contact angle of 0°, so cos (0°) = 1

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Surface tension: the surface tension of a liquid results from cohesive forces between surface molecules.Surface tension is an intensive property.

Surface pressure: the difference between surface tension of different substance.Surface pressure is an extensive property.

BASIC KNOWLEDGE

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Spreading: Spread the solution of surfactant molecule on surface of sub phase dropwise.Procedure: 1,Clean the trough with deionized water three times 2, Soak the filer paper3, Clean the barriers with water and ethanol4, Fill the trough with water and place barriers on trough and hang the paper on hook5, Test the degree of clean of the trough(<0.1)6, If trough is clean, calculate the amount of solution of molecule of interest needed7, Spread the molecule dropwise8, After all of solvent vaporize, the barriers begin compressing9, When compression stop, collect data from computer

Skill and procedure

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Two dimensional phase change

Gaseous phase•molecules in a Langmuir monolayers are very far apart, little intermolecular force.

Liquid phase•closer and stronger lateral interaction•the liquid-expanded (LE) and liquid-condensed (LC) phase. •In LE transition, the isotherms display a considerable curvature at liftoff from = 0 mN/m. •During LC phase, the compressibility of monolayer decreases, and the interaction between tail part of molecule increases.

Solid phase•Headgroups of molecule are dehydrate, tail parts are tightly packed. Strong intermolecular interaction.

Collapse Phase

At this point, monolayer cannot be compressed, and further compression will disrupt the film.

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Collapse phase

16trans-DPPA

cis-DPPAwith guache between hydrogen and alkyl group, and between alkyl group

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Experiment data

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Early data

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DPPA data

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DPPA on salt sub phase

Data obtained:3/22/2016

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Future work-Practice spreading DPPA on salt water to get reproducible data

-Test the DPPA on salt solution with different concentration

-Study DPPA behavior under different pH environment

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Reference

Langmuir. Digital image. Surface Pressure/molecular Area

Isotherms Measured by the Langmuir Method – a

Nanoscience Approach to Study Films at the Water-

air Interface. Web. <http://nano.uib.no/Langmuir.php>

Notter, Robert H. Lung Surfactants: Basic Science and Clinical

Applications. New York: Marcel Dekker, 2000. Print.

DPPA - Structural Formula Illustration. Digital image. Web.

<http://www.rxlist.com/definity-drug.htm>.